Whipple's disease is a systemic bacterial infection and the common though not invariable manifestations are diarrhoea, weight loss, abdominal pain, and arthralgia. Arthritis or arthralgia may be the only presenting symptom, predating other manifestations by years. Virtually all organs in the body may be affected, with protean clinical manifestations. Various immunological abnormalities, some of which may be epiphenomena, are described. The causative organism is Tropheryma whippelii. The disease is uncommon though lethal if not treated. Recent data suggest the disease occurs in an older age group than previously described. The characteristic histopathological features are found most often in the small intestine. These are variable villous atrophy and distension of the normal villous architecture by an infiltrate of foamy macrophages with a coarsely granular cytoplasm, which stain a brilliant magenta colour with PAS. These pathognomonic PAS positive macrophages may also be present in the peripheral and mesenteric lymph nodes and various other organs. The histological differential diagnoses include histoplasmosis and Mycobacterium avium-intercellulare complex. The clinical diagnosis of Whipple's disease may be elusive, especially if gastrointestinal symptoms are not present. A unique sign of CNS involvement, if present, is oculofacial-skeletal myorhythmia or oculomasticatory myorhythmia, both diagnostic of Whipple's disease. A small bowel biopsy is often diagnostic, though in about 30% of patients no abnormality is present. In patients with only CNS involvement, a stereotactic brain biopsy can be done under local anaesthetic. A recent important diagnostic test is polymerase chain reaction of the 16S ribosomal RNA of Tropheryma whippelii. Whipple's disease is potentially fatal but responds dramatically to antibiotic treatment. In this review the current recommended treatments are presented. The response to treatment should be monitored closely, as relapses are common. CNS involvement requires more vigorous treatment because there is a high rate of recurrence after apparently successful treatment.